The object of this research is a stationary diesel engine with one cylinder, Smart Engine Test Bed TD 111 MK II, which was influenced by a magnetic field. The magnet was mounted at the fuel pump channel. The variations of the magnetic flux that use in this experiment are : magnet X (2500 Gauss), magnet Y (2000 Gauss), and magnet Z (350 Gauss). The purpose of this study is to find about the effect of the magnetic field to the performance of the engine. This method of this research is collect the input data by reading all the instrumentation directly, and then calculate it by using Willard Pulkrabek reference. Variations of the static load are : 3,5 kg and 4,5 kg. Variations of the rotation : 1600 rpm, 1800 rpm, 2000 rpm, 2200 rpm, 2400 rpm, 2600 rpm; where the engine use diesel fuel. From the experiment, it was found that magnet X brings the largest effect to the performance of the engine. The magnet X experiment’s result by using 4,5kg static load and 2600 rpm engine rotation: power brake obtained is 3,28 kW, SFC value at 93 g/kWh, AFR value at 52,80, thermal efficiency obtained 21,72% , and heat loss obtained 24,98%.